1. Field of the Invention
This invention is related to the recovery of hydrocarbons from solid carbonaceous materials, and more specifically to an improved process using syn gas and liquid hydrocarbon in a generally horizontal rotary kiln.
2. Background
Worldwide demand for hydrocarbons and related petrochemicals and fertilizers is increasing at a rapid annual rate. Crude petroleum and natural gas are basic in satisfying these demands while at the same time many industries have experienced shortages despite the discovery of new oil and gas sources. Therefore, alternate solid hydrocarbon sources and feed stocks, such as coal, tar sands, oil shale and solid crudes present an ever increasingly attractive source for meeting demand for hydrocarbon products.
Oil shale and tar sands, also known as oil sands and bituminous sands, arc particularly promising sources of these needed products as large deposits are found in Canada and the United States. The largest known deposit of oil shale is the Green River formation in Utah, Colorado and Wyoming with about a third of such deposits in the state of Utah. The hydrocarbon resource locked in the Green River formation has been estimated to be in excess of 1.5 trillion barrels. This is a considerable resource considering known world oil shale reserves amount to just over 2.5 trillion barrels, by conservative estimates.
The demand for hydrocarbon resources makes development of the Green River formation virtually certain. During the 1970s and 1980s several oil shale operations were developed in Colorado and Utah, however due primarily to economic considerations most of these operations have since ceased. An average recovery of about 29 to 34 gallons of oil per ton of oil shale was typical of these previous recovery efforts.
Green River oil shale is a pctroliferous material (heavy viscous oil material) which is as high as 25% by weight with an average of 12% by weight hydrocarbon. The recovered oil is about 17xc2x0-25xc2x0 API gravity, frequently averaging about 21xc2x0, and contains a low amount of sulfur and low aromaticity. The Green River shale has relatively high moisture content of between about 0.4% to 6%. Ranges for analysis of several samples of Green River oil shale are shown in Table 1. The balance of the components, not shown in the table, are made up primarily of various minerals and trace metals.
The largest known deposits of tar sands are the Athabasca sands found in northern Alberta, Canada which underlay more than 13,000 square miles at a depth up to 2,000 ft. Of the 24 states in the United States that contain tar sands, about 90% of such deposits are in the state of Utah. The hydrocarbon resource locked in the Utah tar sands has been estimated to be in excess of 25 billion barrels.
However, the Utah tar sands, being of non-marine origin, have somewhat different chemical and physical characteristics than the Athabascan sands which are of marine origin, and do not respond as well to the traditional process used to extract oil from tar sands. Utah tar sands are generally hard consolidated sand stone closely associated with pctroliferous material (heavy viscous oil material) which is as high as 13% by weight with an average of 10.5% by weight hydrocarbon. The oil is about 13xc2x0-18xc2x0 API gravity and contains a low amount of sulfur, e.g. less than about 0.9% by weight, low aromaticity and a very low water content. The Athabascan sand has an encapsulating water film surrounding each sand grain, which makes it amenable to a water-wetting process. The absence of this water film on the Utah sand grain necessitates using other technology for extracting the oils.
A comparison of the Athabascan tar sands with a sample of Utah tar sands obtained from Asphalt Ridge is shown in Table 2.
The high viscosity, low sulfur content, low water content and other significant differences keep the Utah tar sands from responding well to commonly used extraction processes.
A number of oil recovery methods related to oil shale and tar sands have been tested in the laboratory or in small operations in the field. These processes involve various techniques such as hot water processes, cold water processes, solvent processes, thermal processes and the like, but in most eases, they possess certain limitations which make them unsuitable for use on a commercial basis. Further, many of these processes leave over 20% of the organic carbon behind in the spent shale. A process which would be effective with these particular oil shales and tar sands would be a significant advance in the art.
It is an object of the invention, therefore, to provide a new and efficient process for the extraction of hydrocarbonaceous material from solids containing such material and particularly from Green River oil shale. Another object of the present invention is to provide unique synergies to facilitate the economical production of various products from hydrocarbonaceous solids. It is a further object to provide such an extraction process which could utilize equipment now in commercial use, meet present day EPA standards and could be rapidly put into commercial production to meet the urgent demand for various hydrocarbon products.
It has now been discovered that these and other objects can be accomplished by the process of the present invention which relates to a new and improved process for extracting oil and other valuable hydrocarbons from crushed hydrocarbonaceous solids, such as oil shale, by means of a thermal technique using a special source of heat. The process of the present invention represents an improvement upon U.S. Pat. No. 4,725,350, hereby incorporated by reference in its entirety, and which is also the work of the present inventor.
Specifically, the present invention provides a new and efficient process for extracting valuable oils and other hydrocarbons from crushed hydrocarbonaceous solids which comprises blending the crushed solids to provide a substantially uniform feed composition and preheating the crushed hydrocarbonaceous solids to remove residual water. The crushed solids are treated in a generally horizontal rotary kiln having a slight slope downward with hot syn gas containing hydrogen and carbon dioxide at an elevated temperature and sprayed liquid hydrocarbon in the absence of water. The pressure inside the kiln is maintained below 30 psi and the crushed solids are cascaded into the hot syn gas for sufficient time to strip volatile hydrocarbon containing liquids and gases found in the crushed solids. The hydrocarbon rich vaporized materials, enriched syn gas and spent solids are removed from the kiln and the gaseous products are fractionated into desired fractions.
In a more detailed aspect of the present invention the hot syn gas is introduced into the rotary kiln at a temperature between 1000xc2x0 F. and 2500xc2x0 F. and the crushed solids are preheated to a temperature between 100xc2x0 F. and 350xc2x0 F. to reduce the heating load on the kiln.
In yet a more detailed aspect of the invention the hot syn gas is the product of coal gasification. Further, the enriched syn gas may be used as a starting material for the manufacture of other products such as methanol, ammonia, urea and natural gas or combusted and utilized in a combined-cycle electricity generation step to supplement the heating ad, power needs of the process.
The new process presents distinct advantages over the known processes for extraction of hydrocarbons from oil shale, and is particularly adapted for use in the treatment of oil shale and tar sands obtained from Utah deposits. Particular advantage is found in the fact that Utah oil shale is located near large deposits of coal and facilitating a unique combination of the two techniques of coal gasification and the utilization of the syn gas therefrom directly in the oil shale extraction process. In addition, the use of the special hydrogen and carbon dioxide-containing hot gas effects an upgrading of the products as to yield and quality, e.g. 5 to 25% increase in yield of light ends, e.g. gasoline and lighter fractions, and thus presents a desirable economic advantage. As used herein, all percents are by weight unless specifically identified otherwise. The enriched syn gas has a variety of potential uses, all of which increase the economic and practical utility of the process of the present invention. Among these uses are the production of methanol, ammonia, urea, natural gas and recoverable heat value. Further, gas produced in the process may be used for the production of electricity in a combined-cycle power generation step. This reduces the need for off-site electrical power and minimizes burning so as to reduce atmospheric emissions of harmful gases to well below EPA standards.
Further, no water is present in the reaction zone as any residual water is removed during the preheat stage. This has many advantages, such as lower heat requirement during the reaction in the rotary kiln, as well as improved yield. Furthermore, there would be no need for building expensive dams and other water collection projects prior to the operation of the process. In addition, the process utilizes equipment now in commercial production and does not require specially produced equipment which may require long periods of time for construction.
Finally the process presents an additional economic advantage in that the oil vaporized off the oil shale will be in vapor form and can be sent directly to a fractionating tower for refining, thereby eliminating the expense of reheating the hydrocarbons for fractionation.
Additional features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention.